Cytoplasmic localization of the trypanothione peroxidase system in Crithidia fasciculata

Trypandoxin I (TXNI) and tryparedoxin peroxidase (TXNPx), novel proteins is olated from Crithidia fasciculata, have been reported to reconstitute a try panothione peroxidase activity in vitro (Nogoceke, E.; Gommel, D. U.; Kiess , M.; Kalisz, H. M.; Flohe, L. Biol. Chem. 378:827-836; 1997). Combined wit h trypanothione reductase, they may form an NADPH-fueled trypanothione-medi ated defense system against hydroperoxides in the trypanosomatids. In situ confocal microscopy of antibody-stained TXNI and TXNPx and electron microsc opy of the immunogold labeled proteins revealed their colocalization in the cytosol. Insignificant amounts of the enzymes were detected in the nucleus and vesicular structures, whereas the kinetoplast and the mitochondrion ar e virtually free of any label. Comparison of the PCR product sequences obta ined with genomic and cDNA templates rules out any editing typical of kinet oplast mRNA. Sequence similarities with any of the established maxicircle g enes of trypanosomatids were not detectable. It is concluded that both, TXN I as well as TXNPx are encoded by nuclear DNA and predominantly, if not exc lusively localized in the cytosol. Working in concert with trypanothione re ductase, they can function as an enzymatic system that reduces hydroperoxid es at the expense of NADPH without any impairment of the flux of reduction equivalents by cellular compartmentation. (C) 1999 Elsevier Science Inc.